This invention relates to a multi-disk brake for braking various rotary members of an automatic transmission when gears thereof are shifted.
Conventionally, automatic transmissions for motor vehicles have multi-disk brakes for locking various rotary members when transmission gears are shifted. For example, a second coast brake is used to lock front and rear sun gears, a second brake is used to lock the front and rear sun gears to stop counterclockwise rotation of the same, and a first and reversal brake is used to lock a rear planetary carrier.
Such multi-disk brakes are constructed by interleaving a plurality of disks (hereinafter "lamellae"). The rotary member can be locked by engaging the lamellae with each other so as to utilize the friction therebetween.
The construction of a conventional multi-disk brake will be described below with reference to FIGS. 1 to 3 (Japanese Patent Laid-Open No. 59-137621).
FIGS. 1 and 2 are longitudinal and transverse sectional views of a conventional multi-disk brake illustrating essential portions of the same, and FIG. 3 is a plan view of a retention plate for use in the conventional multi-disk brake.
As illustrated, four outer lamellae 3 to 6 of multi-disk brake 2 are supported in a gear box 1 of the automatic transmission. To support the outer lamellae 3 to 6, a plurality of key grooves 7 and a plurality of drive teeth 8 are alternately formed on the inner peripheral surface of the gear box 1 so as to extend in the axial direction thereof.
Each of the outer lamellae 3 to 6 has engaging teeth 9 formed in its outer peripheral edge. The engaging teeth 9 engage with the key grooves 7 to connect or fix the outer lamellae 3 to 6 and the gear box 1 to each other. As a result, the outer lamellae 3 to 6 and the gear box 1 are inhibited from rotating relative to each other.
Inner lamellae 10 to 13 are disposed between the outer lamellae 3 to 6. The outer lamellae 3 to 6 and the inner lamellae 10 to 13 are positioned alternately in an interleaved manner so as to be capable of engaging with each other by the effect of friction. Each of the inner lamellae 10 to 13 has engaging teeth 14 formed in its inner peripheral edge for engagement with a rotary member (not shown), thereby enabling the rotary member to be locked by the braking effect based on the frictional engagement.
There is a certain gap between the outer peripheral surfaces of the outer lamellae 3 to 6 and the inner peripheral surface of the gear box 1, and the outer lamellae 3 to 6 are freed when the frictional engagement is cancelled to enable a gear shift. At this time, the inner lamellae 10 to 13 continue rotating, and the outer lamellae 3 to 6 are thereby dragged, producing a rotational drag motion within the gap. The outer lamellae 3 to 6 are lifted by this rotational drag motion and thereafter fall by gravity. This movement is repeated and the spline section constituted by the key grooves 7 and the drive teeth 8 inside the gear box 1 and the engaging teeth 9 of the outer lamellae 3 to 6 collide against each other to cause continuous impact noise.
To prevent such a rotational drag motion, a retention member 15 such as that shown in FIG. 3 is interposed between the gear box 1 and the outer lamellae 3 to 6.
The retention member 15 is disposed at the uppermost position in the annular gap formed between the outer peripheral surfaces of the engaging teeth 9 of the outer lamellae 3 to 6 and the inner peripheral surface of the gear box 1.
The retention member 15 is integrally formed by press working from a metallic plate and has a comb-like shape with legs 16 to 19. Protrusive resilient clamping means 20 to 23 are formed in the legs 16 to 19 at positions different from each other in the axial direction. The retention member 15 is inserted into the annular gap and fixed therein by bending resilient clamping means 20 to 23.
The resilient clamping means 20 to 23 of the retention member 15 press the outer lamellae 3 to 6 respectively from above, thereby limiting the extent of movement of the outer lamellae 3 to 6 in the rotational direction to prevent the rotational drag motion thereof.
However, the above-mentioned drag torque is not always negligible. Even if the outer lamellae 3 to 6 are pressed downward by the retention member 15, there is a possibility of the outer lamellae 3 to 6 moving upward by receiving the drag torque.
In such an event, the outer lamellae 3 to 6 moved upward fall by gravity and cause continuous impact noise by repeating the above-mentioned rotational drag motion.
In the case of the conventional multi-disk brake, only one means is known for preventing the outer lamellae 3 to 6 from moving upward by the drag torque. It is based on increasing the spring loading of the resilient clamping means 20 to 23 of the retention member 15 relative to the drag torque to press the outer lamellae 3 to 6 downward by a force larger than the drag torque. In order to set a sufficiently high degree of spring loading of the resilient clamping means 20 to 23, it is necessary to increase the size of the retention member 15 to a large extent. A problem of an increase in the production cost is therefore encountered.
Furthermore, the drag torque varies depending upon the type of the outer lamellae 3 to 6 and the inner lamellae 10 to 13, the distances between the outer lamellae 3 to 6 and the inner lamellae 10 to 13, the rotational speed of the inner lamellae 10 to 13, the temperature of oil, and so on. It is therefore necessary for the retention member 15 to have a complicated shape. For example, to press the outer lamellae 3 to 6 downward respectively, the legs 16 to 19 and the resilient clamping means 20 to 23 are necessary, resulting in an increase in the production cost. If the shape of the retention member 15 is complicated, the operation of placing the retention member 15 in the small gap is very difficult.
In a case where the outer lamellae 3 to 6 are pressed downward by a force larger than the drag torque, the outer lamellae 3 to 6 remain pressed against portions of the gear box 1 on the opposite side and, as a result, at the time of frictional engagement between the outer lamellae 3 to 6 and the inner lamellae 10 to 13 or disengagement of these members form each other, the pressing force causes a resistance to the engagement or disengagement which not only results in failure to smoothly engage or disengage the lamellae but also causes a delay of engagement or disengagement.